S&P downgrades Computer Sciences Corp.

Standard & Poor’s Ratings Services downgraded Falls Church-based Computer Sciences Corp. after the technology services company disclosed it might have to write off the $1.5 billion value of its National Health Service contract in the United Kingdom.

S&P lowered its long-term rating on CSC from A- to BBB+ and is keeping the company on its CreditWatch with negative implications.

CSC is developing and deploying an integrated electronic patient records system as part of the U.K. government’s National Health System IT program.

CSC disclosed last spring that it was negotiating with the NHS on changes to its IT contract after the project was scaled back.

The company said Tuesday that the U.K. government had not approved proposed changes and negotiations will continue into 2012.

CSC said, without agreement on an amended contract, it could be forced to write off the $1.5 billion value of the contract.